The present invention relates to a drum-type transmission configured to change shift steps by: causing the turn of a shift drum to move a shift fork in its axial direction while the shift fork is guided by a guide groove formed in the outer peripheral surface of a drum main body in the circumferential direction; and thereby moving a shifter member.
In this drum-type transmission, a shift drum is installed near a shift fork shaft configured to pivotally support shift forks in a way that the shift forks are movable in the axial direction, with the axial directions of the shift drum and the shift fork shaft oriented in parallel to each other, and with projecting engagement pin portions of the shift forks put in engagement with guide grooves which are formed in the outer peripheral surface of a drum main body in the circumferential direction (see Japanese Patent No. 2515989, for example).
According to Japanese Patent No. 2515989, two shift forks are pivotally supported by the shift fork shaft in a way that the shift forks are slidable in the axial direction and biased by a spring one-way in the axial direction. Furthermore, in the shift drum, two guide grooves with which the projecting engagement pin portions of the two shift forks are in engagement are formed in the outer peripheral surface of a drum main body in the circumferential direction.